Tetralogy of Fallot (TOF)

What Is Tetralogy of Fallot (TOF)?

Tetralogy of Fallot (fah-LO) is a congenital (present at birth) heart defect. In
tetralogy of Fallot (TOF), four related heart defects change the
way blood flows to the lungs and through the heart.

TOF is repaired through open-heart surgery soon after birth or later in infancy.
Some infants need more than one heart surgery. Most babies who are treated do very
well, but will need regular follow-up visits with a heart specialist.

What Happens in Tetralogy of Fallot (TOF)?

In most cases of tetralogy of Fallot, too little blood goes to the lungs. This
low-oxygen (blue) blood then circulates to the rest of the body, and too little
oxygen reaches the body tissues.

Babies with TOF often have cyanosis — a blue or purple
tint to the baby's skin, lips, and fingernails.

If tetralogy of Fallot isn't treated, a child may have:

cyanosis that gets worse

spells where the blood oxygen levels become very low

dizziness, fainting, or seizures

a higher risk of endocarditis, an infection of the inner layer of the heart

high pressure in the right side of the heart that can cause an irregular heartbeat
(an arrhythmia)

Children whose TOF isn't fixed usually become increasingly blue over time and have
difficulty participating in physical activities (like playing sports). Most babies
who have surgery to correct the defect do very well and can participate in normal
kid activities.

How Does Tetralogy of Fallot (TOF) Affect the Heart?

"Tetralogy" means a combination of four related symptoms or problems. The four
problems of tetralogy of Fallot are:

Ventricular septal defect (VSD),
which is a hole in the septum, or wall, separating the two lower chambers, or ventricles,
of the heart. The septum normally acts as a barrier that prevents blood from both
sides of the heart from mixing. But when there is a VSD, the high-oxygen blood from
the left ventricle and the low-oxygen blood from the right ventricle can mix. This
can lead to either too little or too much blood flow going to the lungs. The VSD in
children with TOF is usually large.

Pulmonary stenosis,
a narrowing or thickening of the valve that connects the right ventricle to the pulmonary
artery, the blood vessel that carries low-oxygen blood from the heart to the lungs.
When in the lungs, blood normally soaks up the oxygen that we breathe and becomes
red, oxygen-rich blood. This red blood returns to the heart, and then is pumped to
the body.

With pulmonary stenosis, the heart has to work harder than normal
to pump blood to the lungs. There is also less blood traveling to the lungs because
the pathway is narrowed. This leads to less blood becoming red, oxygen-rich blood.
Sometimes, infants with TOF have pulmonary atresia, where the pulmonary
valve is completely sealed off.

Right ventricular hypertrophy (hi-PER-truh-fee), which is a thickening
of the muscular wall of the right ventricle. The thickened wall can contribute to
blocking the flow of blood through the pulmonary valve, which allows blood from the
heart to flow into the lungs.

An "overriding aorta," which means the artery that carries high-oxygen
blood to the body is out of place and arises above both ventricles, instead of just
the left ventricle, as in a healthy heart. This allows some blood that is low in oxygen
to flow into the aorta and out to the body, instead of to the pulmonary artery, which
would normally take it to the lungs to pick up oxygen.

What Are the Signs of Tetralogy of Fallot (TOF)?

Cyanosis is a very common sign. Healthy babies can sometimes also have bluish skin
around the mouth or eyes from prominent veins under the skin, but their lips and tongue
look pink. Babies who have low oxygen levels in the blood usually have blue lips and
tongues in addition to bluish skin.

A child with TOF might have sudden episodes of deep cyanosis, called "hypercyanotic
spells" or "Tet spells," during crying or feeding. Older children who have Tet spells
will often instinctively squat down, which helps to stop the spell.

"clubbing," where the skin or bones around the tips of fingers are widened or
rounded

What Causes Tetralogy of Fallot (TOF)?

The specific cause of tetralogy of Fallot isn't always known. The TOF changes in
a baby's heart develop in the early weeks of pregnancy. In some cases, there are genetic
causes of TOF — for example, children with Down
syndrome or DiGeorge syndrome are more likely to have TOF. Someone born with TOF
is more likely to have a child or sibling with it. Each year, roughly 1 out of every
2,500 babies born in the United States have the condition.

Babies of mothers who get rubella (German
measles) or other viral illnesses during their pregnancies are at a higher risk
for TOF. Other pregnancy-related risks include poor nutrition, alcohol abuse, poorly
controlled diabetes, and the mother's age (over 40). Certain environmental factors,
such as air pollution, also may increase a mother's chances of having a baby with
TOF.

Most of the time, a child with TOF doesn't have any other birth defects.

How Is Tetralogy of Fallot (TOF) Diagnosed?

Doctors might do several tests to find out if a baby has tetralogy of Fallot and
to get more details about the baby's heart and blood vessels, including:

pulse oximeter:
a small sensor that clips onto the fingertip, toe, or ear and measures how much oxygen
is in the blood. In many newborn nurseries, all babies have a pulse oximeter
test before going home to make sure that their oxygen level is normal.

cardiac catheterization:
a thin, flexible tube called a catheter is inserted into the heart, usually through
a vein in the leg or arm, and provides information about the heart as well as blood
pressure and blood oxygen levels. Sometimes, a device is inserted into the heart or
blood vessels through the heart catheter.

How Is Tetralogy of Fallot (TOF) Treated?

Doctors repair tetralogy of Fallot through open-heart surgery soon after birth
or later in infancy, depending on the baby's health and weight and severity of defects
and symptoms.

The two surgical options are:

Complete repair: The surgeon widens the passageway between the
right ventricle and the pulmonary artery to improve blood flow to the lungs. The ventricular
septal defect is patched to stop the mixing of high-oxygen blood with low-oxygen blood
between the ventricles.

These repairs also fix the two remaining defects
(overriding aorta and right ventricular hypertrophy). Because the right ventricle
doesn't have to work as hard to pump blood into the lungs, the thickness of the ventricle
wall will decrease. And the patched VSD prevents blood with low oxygen from flowing
into the aorta.

Temporary or palliative surgery: Minor repairs can improve blood
flow to the lungs. This usually is done only when a baby is too weak or small to have
full surgery. The surgeon creates a secondary route for blood to travel to the lungs
for oxygen by placing a small tube (called a shunt) between a large artery branching
off the aorta and the pulmonary artery.

The full repair is done later
when the baby grows stronger.

Most babies whose tetralogy of Fallot is repaired do very well, but will need regular
follow-up visits with a heart specialist.